Polyphenylene ether resin (also known as polyphenylene oxide), polyamide resin (also referred to as nylon) and polyester resin are recognized in the art as engineering plastics having excellent high heat distortion temperature, high stiffness and high strength at elevated temperatures. However, these engineering resins have drawbacks such as poor impact strength, poor processability due to high melt strength, high melting and high glass transition temperatures and poor chemical resistance thereby limiting their fields of application.
In an attempt to improve its properties, polyphenylene ether resin has been blended with other resins. For example, U.S. Pat. No. 3,383,435 discloses a composition comprising polyphenylene ether resin and a polystyrene or a rubber-modified styrene resin, wherein the rubber component is a highly unsaturated rubber, such as, polybutadiene.
U.S. Pat. Nos. 3,658,945 and 3,943,191 disclose compositions comprising polyphenylene ether resin and an EPDM-modified styrene resin. In these patents the EPDM rubber replaces the highly unsaturated rubber used in the U.S. Pat. No. 3,383,435 in an attempt to increase the impact strength. However, no significant improvement was achieved.
Other compositions have been disclosed comprising a polyphenylene ether resin and an EPDM-modified styrene resin with additional components. U.S. Pat. No. 4,172,826 discloses compositions comprising polyphenylene ether resin, EPDM-modified styrene resin, hydrogenated A-B-A block copolymers and, optionally, a filler. In U.S. Pat. No. 4,483,958 the composition disclosed comprises polyphenylene ether resin, EPDM-modified styrene resin, an inorganic filler and a thermoplastic elastomer selected from styrene-conjugated diolefin copolymers and styrene polymer grafted polyolefin.
Various blend compositions of polyolefins and polyphenylene ether resins have been made in an attempt to improve properties, such as impact strength, chemical resistance and melt processability of polyphenylene ether resins. For example, U.S. Pat. No. 3,361,851 to Gowan discloses a composition comprising polyphenylene ether resin and polypropylene, wherein a small quantity of polypropylene is dispersed in the polyphenylene ether resin. The reference teaches that the amount of the polypropylene that can be incorporated is limited to no more than 10% by weight of the total composition and that incorporating amounts of polypropylene exceeding 10% results in phase separation during the molding of such compositions and delamination of the molded articles.
It has also been disclosed that larger amounts of polypropylene can be incorporated in polyphenylene ether resin compositions if elastomeric block copolymers are present and, optionally, polystyrene. Compositions of this kind are described in U.S. Pat. No. 4,166,055; 4,764,559 and 4,383,082 and EPA 263678. These patents teach improved compatibility between the polyolefin and polyphenylene ether and improved impact strength However, there is a substantial decrease in flexural modulus and heat distortion temperature.
U.S. Pat. No. 4,713,416 to Del Giudice et al. discloses a composition of (a) polyphenylene ether resin, (b) a thermoplastic copolymer other than polystyrene that is incompatible with polyphenylene ether resins, such as crystalline olefin polymers, polycarbonates, aromatic polyesters and polyamides, and (c) a compatibility promoting agent. When the incompatible thermoplastic copolymer is a crystalline olefin polymer the reference teaches using either (a) block copolymers consisting of a vinyl aromatic monomer and a crystalline olefin or (b) the product obtained by grafting a vinyl aromatic monomer onto a crystalline polymer of a C.sub.2 -C.sub.6 olefin.
European Patent Application 449 087 A2, published Oct. 10, 1991, discloses blend compositions of (a) polyphenylene ether resin, a styrene resin or mixtures thereof, (b) a styrenic grafted propylene polymer material, (c) one or more monoalkenyl aromatic hydrocarbon-conjugated diene block copolymers, hydrogenated products thereof or mixtures thereof, and optionally, (d) a propylene polymer material.
U.S. Pat. No. 4,914,153 discloses modified polyphenylene ether compositions wherein the polyphenylene ether is itself modified with a reactant selected from maleic anhydride, glycidyl methacrylate and glycidyl acrylate; further includes a polyolefin modified with styrene and a modifier selected from maleic anhydride, glycidyl methacrylate and glycidyl acrylate; and a binder selected from a broadly disclosed class of compounds not relevant to the instant invention. The reference discloses a broad concentration range for the polyolefin modifier and vinyl or vinylidene compound used in modifying the polyolefin, 0.01 to 50% by weight (col. 6, lines 10-12). Furthermore, the ratio between the polyolefin modifier and vinyl or vinylidene compound is stated to be in the range of 1 to 90% by weight Referring to the examples of the patent, in particular "Referential Examples" 5, 6 and 7, the amount of bonded styrene was 5 5% and bonded glycidyl methacrylate 0.7%. Referential Example 4 describes the method of producing the modified polypropylene and states that the material was extracted with methyl ethyl ketone. The resulting product therefore differed from the instant invention particularly in the absence of a copolymerized styrenic polymer component. The reference also includes performance properties of the compositions, e.g., tensile strength of polyphenylene ether blends with the modified polypropylene (Tables 1 and 2). The level of tensile strength is substantially less than achieved in the present invention.
Blends of polyester resin, e.g., polybutylene terephthalate blended with a modified polypropylene is disclosed in U.S. Pat. No. 5,004,782. However, the modifier for the polypropylene is limited to an unsaturated carboxylic acid or anhydride thereof (particularly, maleic anhydride, col. 2, lines 30-36) and other blend components absent from the instant invention are also required.
Another type of modified polypropylene is disclosed in U.S. Pat. No. 4,957,974 as useful in blends with e.g., polyesters (col. 12, lines 57-59), polyamides or nylons (col. 13, lines 2-4) and polycarbonates (col. 13, line 6). The essential modifier for the polypropylene in that reference is a graft copolymer of a methacrylic ester, e.g., methyl methacrylate and can include an acrylic or styrenic monomer copolymerizable with the ester, including glycidyl methacrylate (col. 7, line 68).